The surface strength of web material particularly paper is generally determined off-line (off the paper machine) using some form of adhesive or sticky medium which is applied to the web and the amount of material removed from the surface of the web by the sticky material provides an indication of surface strength or linting propensity of the web.
One way of doing such a test is to use a commercial offset press (e.g. an Apollo press) the paper is printed and the amount of lint accumulating on the printing blanket over a period of time is measured to provide an indication of the linting propensity.
Other techniques are utilized for example, in one technique a wet blanket is moved against the web and over a period of time, the lint accumulated and doctored off the blanket, is filtered and weighed to provide an indication of the linting propensity. In another technique a steel roller wetted with a picking oil is used to pull lint from the web and the amount of lint accumulated on the roller over time is measured to provide an indication of linting propensity.
It is also known to apply a brushing action to the sheet, for example, over the impression roller and collect the lint freed from the web using a vacuum. This lint is subsequently weighed to provide an indication of linting propensity.
In another vacuum system lint is simply vacuumed from the web on the press stand using a vacuum nozzle to clean a given area of the paper surface, the lint so collected is then examined to provide an indication of linting.
Examples of pick tests include the Dennison wax process wherein tack graded waxes are used. The melted wax of a known tack is pressed firmly into the paper and then after solidifying is pulled away and the paper examined for defects. Papers are graded on the basis of the highest tack wax that can be used without damaging the sample.
The IGT (Instituut voor Grafiske Techniek) pick test is similar to an Apollo test in that it utilizes a small printing unit, however, in this case printing is done under controlled pressure and oil film thickness. The speed of printing is gradually increased. The printed strips are examined under a microscope to determine the speed at which the first sign of surface disruption occurred, i.e. at what speed is the paper able to be printed without surface disruption.
The GFL (Grafiska Forsknining Laboratoriet i Sverige) test is similar to the IGT test but uses an inclined plane and a weighted printing roller to print a sheet. The printed sheet is then examined using low angle light to find the first signs of picking.
In a publication entitled `The Characterization of Offset Lint and the Testing of Offset Papers` by Browning and Parker from the Proceedings of the Symposium on Mechanical Pulp held in Oslo June 22-24, 1970 various techniques or measuring linting characterization of a paper web are described and the effect of applying a brush and a vacuum to remove lint material from the surface of a paper web is described.